Thirty-nine delegates signed the United States Constitution on September 17, 1787.
The signatures were added at Independence Hall in Philadelphia during the final meeting of the Constitutional Convention. The convention had included more participants over its four-month course, but only 39 delegates endorsed the finished document.
George Washington, who chaired the convention, signed first. Benjamin Franklin, James Madison, Alexander Hamilton, and other prominent delegates also signed. Three delegates present at the final session—George Mason, Edmund Randolph, and Elbridge Gerry—refused to sign.
The figure 39 is sometimes confused with the total number of convention delegates or with the 55 delegates who attended at some point. The number of signers refers specifically to delegates whose names were placed on the final Constitution.